Apparatus for Void-Free Debulking of Adhesive Bonded Joints

ABSTRACT

Methods and apparatus for fabricating adhesive bonded joints while minimizing the voids and/or porosity found in the cured bondline. In accordance with various embodiments, the apparatus comprises an evacuation chamber combined with a pressure inducing device to produce bonded joints that are both void free and thoroughly compacted. The surfaces to be bonded are continuously evacuated throughout the bonding process (pre-mating, mating, debulking and cure). Continuous evacuation is provided via standard vacuum, while the induced pressure can be pneumatically or mechanically provided.

RELATED PATENT APPLICATIONS

This application is a divisional of and claims priority from U.S. patentapplication Ser. No. 13/557,269 filed on Jul. 25, 2012, which in turn isa divisional of and claims priority from U.S. patent application Ser.No. 12/953,532 filed on Nov. 24, 2010 (issued on Sep. 11, 2012 as U.S.Pat. No. 8,262,841).

BACKGROUND

This disclosure generally relates to systems and methods for minimizingthe voids and/or porosity of bonded joints (e.g., bonded aircraftjoints) fabricated using adhesives. As used herein, the term “adhesive”comprises resins, film adhesives and paste adhesives.

Known methods of fabricating bonded joints using paste adhesives leavevoids and/or porosity in the bondline once the laminates are bondedtogether. These voids reduce the mechanical properties that, optimally,should be exhibited by the adhesive. This reduction in properties isespecially true for paste adhesives with higher viscosities that tend toretain entrapped air more than less viscous adhesives.

It is known that the application of positive pressure in an autoclavecan be used to reduce the size of voids by reducing their volume. Inmany cases autoclaves are not feasible for use, so vacuum bag processesare used. The resulting bonded repairs were either used as-is withporosity and/or voids, or they were reprocessed until acceptable jointswere fabricated.

There is a need for a solution for eliminating or minimizing voids andporosity in the bondlines of paste adhesive, film adhesive or resinsystem coupons without the use of high-pressure autoclaves.

SUMMARY

This disclosure encompasses methods and apparatus for fabricatingadhesive bonded joints while minimizing the voids and/or porosity foundin the cured bondline. In accordance with various embodiments, theapparatus comprises an evacuation chamber combined with a pressureinducing device to produce bonded joints that are both void free andthoroughly compacted. The surfaces to be bonded are continuouslyevacuated throughout the bonding process (pre-mating, mating, debulkingand cure). Typical atmospheric vacuum and pneumatic pressures are allthat are needed; unusual processes and expensive apparatus are notrequired.

Continuous evacuation is provided via standard vacuum, while the inducedpressure can be pneumatically or mechanically provided. In onemanifestation, the pressure inducing device operates in conjunction witha hinge mechanism that is supported by a collapsible block that iscrushable under slight pressure. (The collapsible block can be a papercup, deflectable balloon, mechanical device or electronic device.) Othermanifestations utilize pneumatic or mechanical apparatus as pressureinducing devices. Potential applications for this invention includeaircraft bonded structure, bonded test specimens or coupons, bondedprecured patches, and/or bonded uncured patches. The processes disclosedherein can be applied to composite and metallic bonded joints.

Other aspects of the invention are disclosed and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a sectional view of apparatus for void-freedebulking of adhesive applied to upper and lower components to be bondedin accordance with one embodiment of the invention. The apparatus isshown in a state wherein the external bag is semi-inflated while thepressure inducer is deflated.

FIG. 2 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral 2in FIG. 1.

FIG. 3 is a drawing showing a sectional view of the apparatus depictedin FIG. 1 in a state wherein the external bag is evacuated while thepressure inducer is deflated.

FIG. 4 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral 4in FIG. 3.

FIG. 5 is a drawing showing a sectional view of the apparatus depictedin FIGS. 1 and 3 in a state wherein the external bag is evacuated whilethe pressure inducer is inflated.

FIG. 6 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral 6in FIG. 5.

FIG. 7 is a free body diagram showing the estimated forces exerted onexemplary apparatus parts and components to be bonded in the statedepicted in FIG. 5.

FIG. 8 is a drawing showing a sectional view of apparatus for void-freedebulking of adhesive applied to an aircraft structure and to a repairpatch to be bonded thereto in accordance with another embodiment of theinvention. The apparatus is shown in a state wherein the external bag issemi-inflated while the pressure inducer is deflated.

FIG. 9 is a drawing showing a sectional view of apparatus for void-freedebulking of adhesive applied to an aircraft structure and to a repairpatch to be bonded thereto in accordance with a further embodiment ofthe invention. The apparatus is shown in a state wherein the externalbag is semi-inflated while the pressure inducer is deflated.

FIG. 10 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral10 in FIG. 9.

FIG. 11 is a drawing showing a sectional view of the apparatus depictedin FIG. 9 in a state wherein the external bag is evacuated while thepressure inducer is deflated.

FIG. 12 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral12 in FIG. 11.

FIG. 13 is a drawing showing a sectional view of the apparatus depictedin FIGS. 9 and 11 in a state wherein the external bag is evacuated whilethe pressure inducer is inflated.

FIG. 14 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral14 in FIG. 13.

FIG. 15 is a free body diagram showing the estimated forces exerted onexemplary apparatus parts and components to be bonded in the statedepicted in FIG. 13.

FIGS. 16A-16D are diagrams showing the sequence of operations forlocating a template and an evacuation chamber in accordance with theembodiment depicted in FIG. 9.

FIG. 17 is a drawing showing a sectional view of apparatus for void-freedebulking of adhesive applied to an aircraft structure and to a repairpatch to be bonded thereto in accordance with yet another embodiment ofthe invention. The apparatus is shown in a state wherein the externalbag is evacuated while the pressure inducer is de-activated.

FIG. 18 is a drawing showing a magnified view of the structureencompassed by the dashed closed contour labeled with boldface numeral18 in FIG. 17.

FIG. 19 is a drawing showing a sectional view of the apparatus depictedin FIG. 17 in a state wherein the external bag is evacuated while thepressure inducer is activated.

FIG. 20 is a drawing showing a magnified view of stack of componentsbeing pressed together by the pressure inducer as seen in FIG. 19.

FIG. 21 is a free body diagram showing the estimated forces exerted onexemplary apparatus parts and components to be bonded in the statedepicted in FIG. 19.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

Various embodiments of the invention will now be described. In eachembodiment, the apparatus used to carry out the debulking processcomprises an evacuation chamber combined with a pressure inducing deviceto produce bonded joints that are both void free and thoroughlycompacted. The surfaces to be bonded are continuously evacuatedthroughout the bonding process (pre-mating, mating, debulking and cure).Continuous evacuation is provided via standard vacuum, while pressurecan be pneumatically or mechanically induced.

To begin the process, parent laminates should be fabricated from thematerial of choice. These laminates could be a metallic structure,carbon/epoxy system, fiberglass/epoxy system, polyimide, or bismalemide.Once these panels are fabricated, surface preparation must be completedto ensure a required bonding surface. If the process is utilized as anon-aircraft or on-part process, the removal of old damage or surfacers(e.g., paint or primer) should be completed prior to surfacepreparation. The surface preparation will include sanding the bondingsurfaces with 150-grit sanding disc or as required by processspecifications. This reactivates the bonding surface and removesoxidation from the surface that hinders the bonding process. The panelswill be wiped clean with acetone or a solvent required per materialspecification until no residue is present. Once the panels or repairpatch and parent structure are prepped and cleaned, the apparatusdisclosed hereinafter is assembled.

In accordance with a first embodiment shown in FIG. 1, the debulkingsystem comprises a frame 2 which is designed to sit on a base plate 4.The frame 2 comprises a strongback support tooling 8 supported along itsperimeter by a solid silicone standoff or spacer 10 connected to andprojecting downward from the perimeter of strongback support tooling 8.The strongback support tooling 8 is made of stiff material, such as apanel made of honeycomb composite material. If the base plate 4 is flat,then the strongback support tooling 8 is preferably flat. Alternatively,an inflatable outer bladder can be used in place of the solid spacer 10.Such an inflatable outer bladder is disclosed in U.S. patent applicationSer. No. 12/894,691 filed on Sep. 30, 2010, the disclosure of which isincorporated by reference herein in its entirety.

An inflatable bladder 20 is removably attached (e.g., by hook-and-loopfasteners) to the interior surface of the strongback support tooling 8and to the upper portions of the interior surface of spacer 10. Thespace bounded by base plate 4, bladder 20 and the lower portion of theinterior surface of spacer 10 will be referred to herein as anevacuation chamber 6. It should be understood that the shape and volumeof the evacuation chamber 6 will change as bladder 20 inflates ordeflates.

In addition to the bladder inside the frame, a heavy breather cloth 16overlies the frame 2 and extends beyond the footprint of frame 2 so thatthe outermost peripheral portion of the breather cloth 16 lies on thebase plate 4. As used herein, the term “breather” means a porousmaterial that serves as a continuous air path over or around the frame2.

In turn, an external vacuum bag 12, made, e.g., of nylon vacuum baggingmaterial, covers the breather material 16. The external vacuum bag 12 issealed to the base plate 4 by sealing tape 14 which surrounds thebreather material 16. In an unevacuated state, the external vacuum bag12 fits loosely over the breather material 16, leaving open spacetherebetween. That open space external to frame 2 communicates freelywith the evacuation chamber 6 via a plurality of throughholes 18 formedin spacer 10. Alternatively, if the interface between base plate 4 andspacer 10 is not airtight due to the presence of one or more gaps,throughholes need not be provided.

The embodiment shown in FIG. 1 further comprises a breather cloth 30which is disposed inside the evacuation chamber 6. The breather cloth 30is placed over a portion of base plate 4 and lower portions of theinterior surface of spacer 10, the latter extending to an elevationhigher than the elevation of throughholes 18. The breather cloth 30helps to maintain the vacuum pressure inside evacuation chamber 6 whenbladder 20 is inflated (see FIG. 5). Optionally, the breather cloth mayalso cover the upper/lower component assembly disposed inside theevacuation chamber 6. In accordance with a further alternative, a solid(i.e., not perforated) sheet of fluorinated ethylene propylene (FEP)film (not shown in FIG. 1) may be laid over the upper/lower componentassembly to prevent the adhesive squeeze out from damaging the innerbladder 20 once it has been inflated (see FIG. 5). This solid FEP sheetwill act as a barrier only.

The evacuation chamber 6 can be coupled to a vacuum source (not shown)by means of a vacuum probe 22 that passes through an opening in theexternal vacuum bag 12 and is connected to the vacuum source by a hose24. Another vacuum probe (not shown in FIG. 1) is coupled to a vacuumgauge (also not shown), which measures the pressure inside theevacuation chamber 6.

In contrast, the bladder 20 can be selectively coupled to either avacuum source (not shown) or to a source of pressurized air (not shown)via a valve 26. FIG. 1 shows the bladder 20 deflated (compare FIG. 5,wherein bladder 20 is inflated). The upwardly directed arrow above valve26 in FIG. 1 indicates the direction of air flow during deflation ofbladder 20, i.e., valve 26 is in a state wherein bladder 20 is coupledto the vacuum source. The valve 26 passes through respective openings inbladder 20, strongback support tool 8 and external vacuum bag 12. Theportion of external vacuum bag 12 surrounding the opening for thepressurization hose which is coupled to valve 26 is sealed around thehose using sealing tape 28.

In the embodiment shown in FIG. 1, two components 32 and 34 to beadhesively bonded together are disposed inside the evacuation chamber 6.These components are shown on a magnified scale in FIG. 2. As seen inFIG. 2, each component has a layer of adhesive 48 applied on a bondingsurface. Alternatively, adhesive could be applied to the bonding surfaceof the lower component 32 only or of the upper component 34 only. In apreferred embodiment, both components are made of fiber-reinforcedplastic material.

Still referring to FIG. 2, lower component 32 is removably attached to alower caul plate 36, while upper component 34 is removably attached toan upper caul plate 38. For example, components 32 and 34 could beattached to the respective caul plates using double-sided adhesive tapethat can be peeled off easily upon completion of the bonding process.The lower caul plate 36 is removably attached to a lower heating blanket40, which in turn is removably attached to base plate 4.

In the embodiment shown in FIGS. 1 and 2, an upper heating blanket 50 isremovably attached to the upper surface of the upper caul plate 38. Asseen in FIG. 1, the upper caul plate 38, with upper component 34 andupper heating blanket 50 attached thereto, is supported at one end by acollapsible block 46 and at the other end by a hinge block 44.Preferably, the collapsible block is made of a material that provides aknown uniform rate of compressive collapse, thereby controlling theinterface contact rate at the adhesive interface. Preferably, the otherend of the upper caul plate 38 is pivotably mounted to hinge block 44 bymeans of a living hinge 42. The hinge block 44 is removably attached tothe base plate 4. Alternatively, a separate hinge could be installedhaving one hinge part attached to the upper caul plate and the otherhinge part attached to the hinge block. In accordance with a furtheralternative, the upper caul plate and hinge block could be coupled bytemporary quick-release fastener means, such as a hook-and-loop fasteneror opposing layers of cohesive material.

In accordance with a further alternative embodiment, caul plateextenders could be attached using double-sided adhesive tape to theupper surface of the upper caul plate 38, the ends of these caul plateextenders in turn being taped to the base plate 4 (using double-sidedadhesive tape), thereby eliminating the need for hinge block 44 shown inFIG. 1. In accordance with this further alternative embodiment, the useof double-sided adhesive tape provides a pivot capability that allowsthe upper caul plate to swing downwardly relative to the base plate whenthe collapsible block 46 collapses. An additional caul plate extendercould be removably attached to the upper surface of the upper caul platesuch that the extender extends beyond the edge of the upper caul plate.The portion of this additional extender which extends beyond the uppercaul plate edge can then be placed on top of the collapsible block 46,so that the upper caul plate itself need not extend all the way to thecollapsible block.

As seen in FIG. 1, the leftmost portion of upper caul plate 38 issupported by a collapsible block 46. The height of collapsible block 46is greater than the height of hinge block 44, so that the upper caulplate 38 will be disposed at an angle with respect to the lower caulplate 36. The blocks 44 and 46 also support upper caul plate 38 in aposition such that there is a gap separating the layers of adhesive 48(see FIG. 2) applied on respective surfaces of the components to bebonded. The collapsible block 46 allows the upper component 34 to matewith the lower component 32 when additive pressure is present (describedin detail below). As previously described, the collapsible blockpreferably provides a known uniform rate of compressive collapse, suchas a block of sponge material. Alternatively, the collapsible block maycomprise a compression spring.

FIG. 1 shows the apparatus upon completion of the initial set-up. FIGS.3 and 4 show the same apparatus as air is being removed from theevacuation chamber 6. Air is removed by pulling a vacuum pressure of14.7 psi on the outer bag 12. As previously explained, the vacuum sourceis coupled to the evacuation chamber 6 via hose 24, vacuum probe 22,breather material 16 and throughholes 18. The vacuum pressure insidechamber 6 causes entrapped air and volatiles to be removed from theadhesive 48 and the space between the two bonding surfaces. The flow ofair and volatiles during evacuation is indicated by arrows in FIG. 3.The goal is to minimize the amount of air and volatiles entrapped in thebondline after the adhesive has been cured. If the entrapped air andvolatiles are not completely evacuated from the bondline surfaces,porosity and voids will be present in the bondline after curing of theadhesive. FIG. 4 is a magnified view of a portion of FIG. 3, showingentrapped air and volatiles leaving the adhesive 48 and flowing out ofthe space separating the lower and upper components 32 and 34.

In accordance with one preferred embodiment, the vacuum pressure staysconstant at 14.7 psi throughout the entire process. This vacuum pressureis applied while the upper and lower components are separated as seen inFIG. 4 for a period of time sufficient to remove air and volatiles fromthe adhesive. When the desired degree of air/volatiles removal has beenachieved, an additive pressure (preferably at least 5 psi) is induced byinflating bladder 20 (i.e., by releasing the retraction vacuum), asshown in FIG. 5. During this operation, the vacuum pressure insidechamber 6 is maintained.

As bladder 20 inflates, it presses against the portion of upper caulplate 38 which is seated atop the collapsible block 46, thereby applyinga downward pressure on the latter to cause its collapse. The collapsibleblock 46 could be a paper cup, compression spring, deflatable ball,sponge, or any other object that will crush under pressure greater than5 psi. As the collapsible block 46 collapses, the upper component 34pivots downward about hinge 42 until it mates with the lower component32. As bladder 20 continues to apply pressure, the adhesive 48 appliedon the respective bonding surfaces of components 32 and 34 is pressedtogether for bondline cure as shown in FIG. 6, which is a magnified viewof a portion of FIG. 5.

After the upper and lower components are pressed together with adhesivetherebetween, the adhesive is ready for cure. The cure cycle can be doneat room temperature or at some elevated temperature, depending on therequirements of the adhesive system. In accordance with the embodimentdepicted in FIGS. 1-6, heating blankets 40 and 50 are used to raise thetemperature of adhesive 48 to a level higher than room temperature. Foradhesives that can be cured at room temperature, heating blankets wouldnot be needed.

In cases where the adhesive is cured at an elevated temperature, atemperature controller (not shown in FIGS. 1-6) is connected to the heatblankets 40 and 50 and to a plurality of strategically placedthermocouples (not shown). In a well-known manner, the temperaturecontroller can be programmed to control the electrical power beingsupplied to the electric heat blankets as a function of the temperaturesdetected by the thermocouples in accordance with a desired temperaturecycle.

FIG. 7 is a free body diagram showing the estimated forces exerted onapparatus parts and components to be bonded in the state depicted inFIGS. 5 and 6 for the exemplary case wherein the strongback supporttooling 8 is a square 18 inches on each side; upper caul plate 38 is asquare 12 inches on each side; and the upper and lower components aresquares 6 inches on each side. In this example, the resulting estimatedcompaction pressure P₃=132.3 psi.

In accordance with another embodiment (the initial set-up for which isshown in FIG. 8), a similar apparatus can be used to bond a composite(i.e., fiber-reinforced plastic) repair patch 56 to a portion of aparent structure (e.g., an aircraft structure) 52 that requires repair.The parent structure 52 may be made of fiber-reinforced plastic ormetallic material. Preferably, the strongback support tooling 8 iscontoured to generally match the contour of the parent structure 52 inthe area of the repair.

In accordance with the embodiment shown in FIG. 8, the area on theparent structure which requires repair must first undergo theappropriate surface preparation. The prepared surface of the repair areaon parent structure 52 is then covered with adhesive 48. Likewise thebonding surface of the repair patch 56 is covered with adhesive 48. Therepair patch 56 is removably attached to one side of an upper caul plate38. A heating blanket 50 is removably attached to the other side ofupper caul plate 38. During set-up, the upper caul plate 38 (withattachments) is placed with one side supported by hinge block 44 (viahinge 42) and the other side supported by collapsible block 46 having aheight greater than the height of the hinge block. The heights of thehinge block and collapsible block are selected so that the upper caulplate 38 is disposed at an angle relative to the parent structure 52 andthe adhesive 48 on the surface of repair patch 56 is separated by a gapfrom the adhesive 48 applied on the repair area of the parent structure52. Then the evacuation chamber frame 2 (with attachments) is placed asseen in FIG. 8. The breather material 16 is then placed as seen in FIG.8. Finally, the external vacuum bag 12 is placed over the breathermaterial 16 and sealed to the parent structure 52 by sealing tape 14.Other structural elements shown in FIG. 8 are indicated by the samereference numerals (e.g., 8, 10, 18, 22, 24, 26, 28 and 30) used forcorresponding structural elements previously described with reference toFIG. 1.

To bond the repair patch 56 to the parent structure 52, the same processsteps, as previously described, are performed in sequence, namely: (1)chamber 6 is evacuated, the vacuum pressure being maintained for a timesufficient to extract air and volatiles from the uncured adhesive; (2)after air and volatiles have been removed from the adhesive and whilethe vacuum pressure in chamber 6 is still being maintained, bladder 20is inflated, first causing collapsible block 46 to collapse and thencausing repair patch 56 to be pressed against the parent structure 52with adhesive 48 therebetween; and (3) while the vacuum pressure inchamber 6 and the additive pressure of inflated bladder 20 aremaintained, heating blanket 50 is activated to heat adhesive 48 to itscure temperature. Following these steps, all of the equipment (excludingrepair patch 56) is removed, leaving the repair patch 56 adhesivelybonded to the parent structure 52. The surface of the repair area withrepair patch can then be finished according to required specifications.

FIG. 9 is a sectional view of apparatus for void-free debulking ofadhesive 48 applied to a parent structure 52 (e.g., an aircraftstructure) and to a repair patch 56 to be bonded thereto in accordancewith a further embodiment of the invention. In a preferred embodiment,both the repair patch and parent structure are made of fiber-reinforcedplastic material. In FIG. 9, the apparatus is shown in a state whereinthe external bag 12 is semi-inflated while the pressure inducer 20 isdeflated. FIG. 10 shows a magnified view of the structure encompassed bythe dashed closed contour labeled with boldface numeral 10 in FIG. 9.

In accordance with the embodiment depicted in FIGS. 9 and 10, the areaon the parent structure 52 which requires repair must first undergo theappropriate surface preparation. A component alignment template 54 isthen placed on the top surface of the parent structure 52, surroundingthe repair area (the shape of component alignment template 54 is shownin FIG. 16B). Still referring to FIGS. 9 and 10, the prepared surface ofthe repair area on parent structure 52 is then covered with adhesive 48.

An evacuation chamber frame with attachments is then placed over therepair area (now covered by adhesive). The frame comprises a strongbacksupport tooling 8 supported along its perimeter by a solid siliconestandoff or spacer 10 connected to and projecting downward from theperimeter of strongback support tooling 8. The spacer 10 has a pluralityof throughholes 18. The strongback support tooling 8 has a throughholein which a valve 26 is installed.

The shape of the inner periphery of spacer 10 is designed to match theouter periphery of the component alignment template 54, which will bedescribed in more detail later with reference to FIGS. 16A-16D. Theevacuation chamber frame is in proper position when it is placed on theparent structure 52 in a position where component alignment template 54fits within the inner periphery of spacer 10.

The evacuation chamber frame has various attachments. An inflatablebladder 20 is removably attached (e.g., by hook-and-loop fasteners) tothe interior surface of the strongback support tooling 8. The interiorvolume of the bladder 20 is in fluid communication with the valve 26.The space bounded by parent structure 52, bladder 20 and the lowerportion of the interior surface of spacer 10 forms an evacuation chamber6. As previously explained, the shape and volume of the evacuationchamber 6 will change as bladder 20 inflates or deflates.

The bladder 20 supports a stack of components (see items 50, 38 and 56in FIG. 10). An upper heating blanket 50 is removably attached (e.g.,using double-sided adhesive tape) to the external surface of bladder 20;an upper caul plate 38 is removably attached (e.g., using double-sidedadhesive tape) to the lower surface of upper heating blanket 50; and therepair patch 56 is removably attached (e.g., using double-sided adhesivetape) to the lower surface of upper caul plate 38. The bonding surfaceof the repair patch 56 is covered with adhesive 48.

After the evacuation chamber frame has been placed on top of the parentstructure 52, the frame is covered with a heavy breather cloth 16. Thebreather cloth 16 overlies the external surface of strongback supporttool 8 and the external surface of spacer 10. Most importantly, thebreather cloth 16 must overlie the throughholes 18 in spacer 10.

The breather material 16 is then covered with an external vacuum bag 12,made, e.g., of nylon vacuum bagging material. The external vacuum bag 12is sealed to the parent structure 52 by sealing tape 14 which surroundsthe evacuation chamber frame. The external vacuum bag 12 has an openingin which a vacuum probe 22 is installed. The vacuum probe 22 isconnected to a vacuum source by a hose 24. The evacuation chamber 6 canbe coupled to the vacuum source via hose 24, probe 22, breather cloth16, and throughholes 18. Another vacuum probe (not shown in FIG. 9) canbe coupled to a vacuum gauge (also not shown), which measures thepressure inside the evacuation chamber 6. The portion of external vacuumbag 12 surrounding the opening for the pressurization hose which iscoupled to valve 26 is sealed around the hose using sealing tape 28. Inan unevacuated state, the external vacuum bag 12 fits loosely over thebreather material 16, leaving open space therebetween. FIG. 9 shows theexternal vacuum bag 12 when the chamber 6 is evacuated.

Still referring to FIG. 9, the bladder 20 can be selectively coupled toeither a vacuum source (not shown) or to a source of pressurized air(not shown) via valve 26. FIG. 9 shows the bladder 20 deflated (compareFIG. 13, wherein bladder 20 is inflated). The upwardly directed arrowabove valve 26 in FIG. 9 indicates the direction of air flow duringdeflation of bladder 20, i.e., valve 26 is in a state wherein bladder 20is coupled to the vacuum source.

In the embodiment shown in FIG. 9, a repair patch 56 to be adhesivelybonded to the parent structure 52 is disposed inside the evacuationchamber 6. These components are shown on a magnified scale in FIG. 10.As seen in FIG. 10, respective layers of adhesive 48 are applied toconfronting surfaces of parent structure 52 and repair patch 56.Alternatively, adhesive could be applied to parent structure 52 only orto repair patch 56 only.

FIG. 9 shows the apparatus upon completion of the initial set-up. FIGS.11 and 12 show the same apparatus as air is being removed from theevacuation chamber 6. Air is removed by pulling a vacuum pressure of14.7 psi on the outer bag 12. The vacuum pressure inside chamber 6causes entrapped air and volatiles to be removed from the adhesive 48and the space between parent structure 52 and repair patch 56. The flowof air and volatiles during evacuation is indicated by arrows in FIG.11. FIG. 12 is a magnified view of a portion of FIG. 11, showingentrapped air and volatiles leaving the adhesive 48 and flowing out ofthe space separating parent structure 52 and repair patch 56.

In accordance with one preferred embodiment, the vacuum pressure staysconstant at 14.7 psi throughout the entire process. This vacuum pressureis applied while parent structure 52 and repair patch 56 are separatedas seen in FIG. 12 for a period of time sufficient to remove air andvolatiles from the adhesive. When the desired degree of air/volatilesremoval has been achieved, an additive pressure (preferably at least 5psi) is induced by inflating bladder 20 (i.e., by releasing theretraction vacuum), as shown in FIG. 13. During this operation, thevacuum pressure inside chamber 6 is maintained.

As bladder 20 inflates, the repair patch 56 is displaced downward andpressed against parent structure 52. As bladder 20 continues to applypressure, the adhesive 48 applied on the respective confronting surfacesof parent structure 52 and repair patch 56 is pressed together forbondline cure as shown in FIG. 14, which is a magnified view of aportion of FIG. 13.

After parent structure 52 and repair patch 56 are pressed together withadhesive 48 therebetween, the adhesive is ready for cure. The cure cyclecan be performed at room temperature or at some elevated temperature,depending on the requirements of the adhesive system. In accordance withthe embodiment depicted in FIGS. 9-14, heating blanket 50 is used toraise the temperature of adhesive 48 to a level higher than roomtemperature. For adhesives that can be cured at room temperature, aheating blanket would not be needed.

In summary, to bond the repair patch 56 to the parent structure 52, thesame process steps, as previously described, are performed in sequence,namely: (1) chamber 6 is evacuated, the vacuum pressure being maintainedfor a time sufficient to extract air and volatiles from the uncuredadhesive; (2) after air and volatiles have been removed from theadhesive and while the vacuum pressure in chamber 6 is still beingmaintained, bladder 20 is inflated, causing repair patch 56 to bepressed against the parent structure 52 with adhesive 48 therebetween;and (3) while the vacuum pressure in chamber 6 and the additive pressureof inflated bladder 20 are maintained, heating blanket 50 is activatedto heat adhesive 48 to its cure temperature. Following these steps, allof the equipment (excluding repair patch 56) is removed, leaving therepair patch 56 adhesively bonded to the parent structure 52. Thesurface of the repair area with repair patch can then be finishedaccording to required specifications.

FIG. 15 is a free body diagram showing the estimated forces exerted forthe exemplary case wherein the strongback support tooling 8 shown inFIG. 13 is a square 16 inches on each side and upper caul plate 38 is asquare 12 inches on each side. In this example, the resulting estimatedcompaction pressure P₂=26.1 psi.

FIGS. 16A-16D show the sequence of operations for locating a componentalignment template 54 and an evacuation chamber frame 2 in accordancewith the embodiment depicted in FIG. 9.

In a first step (shown in FIG. 16A), the location where the adhesivesystem and repair patch will be placed on the parent structure 52 issketched out and the component alignment template 54 is placed on parentstructure 52 in alignment with the sketched circle.

In a second step (shown in FIG. 16B), adhesive 48 is placed on parentstructure 52 inside component alignment template 54. The componentalignment template 54 is used to control adhesive squeeze out andbondline thickness.

In a third step (shown in FIG. 16C), the evacuation chamber frame 2 isplaced on parent structure 52 in a position dictated by the componentalignment template 54, thus ensuring that the repair patch carriedinside evacuation chamber frame 2 will be aligned with adhesive 48 whichis bounded by component alignment template 54.

In a fourth step (shown in FIG. 16D), the repair patch will be stuck tothe top of the evacuation chamber with double-sided adhesive tape, forexample, and will be applied to the repair area after the evacuationprocess has been completed and the inner bladder has been pressurized,pressing the repair patch against the parent structure 52 with adhesivetherebetween.

FIG. 17 is a sectional view of apparatus for void-free debulking ofadhesive 48 applied to a parent structure 52 (e.g., an aircraftstructure) and to a repair patch 56 to be bonded thereto in accordancewith yet another embodiment of the invention. In a preferred embodiment,both the repair patch and parent structure are made of fiber-reinforcedplastic material. The apparatus seen in FIG. 17 differs from that shownin FIG. 9 in that the upper heating blanket 50 is removably attached toa tooling pressure plate 74 of a mechanical pressure inducer 60 insteadof to an inflatable bladder. Because the internal bladder is notpresent, the evacuation chamber will be the volume bounded by theevacuation chamber frame and the parent structure 52.

The mechanical pressure inducer 60 further comprises a member 62 whichis affixed to the lower surface of the strongback support tool 8, amember 66 having one end pivotably coupled to one end of member 62 andanother end pivotably coupled to one end of a member 68, and a member 70having one end pivotably coupled to another end of member 62 and anotherend pivotably coupled to one end of a member 72. The other ends ofmembers 68 and 72 are respectively pivotably coupled to opposite ends ofa member 64 to which tooling pressure plate 74 is attached. Themechanical pressure inducer 60 is designed to alternately extend andretract in response to activation of a driving mechanism (not shown).The drive mechanism may, for example, be a lead screw of a screw jack,some other screw mechanism, a piston or a solenoid. FIG. 17 shows themechanical pressure inducer 60 in a retracted state; FIG. 19 shows themechanical pressure inducer 60 in an extended state.

As best seen in FIG. 18, the tooling pressure plate 74 supports a stackof components. An upper heating blanket 50 is removably attached (e.g.,using double-sided adhesive tape) to the lower surface of toolingpressure plate 74; an upper caul plate 38 is removably attached (e.g.,using double-sided adhesive tape) to the lower surface of upper heatingblanket 50; and the repair patch 56 is removably attached (e.g., usingdouble-sided adhesive tape) to the lower surface of upper caul plate 38.The bonding surface of the repair patch 56 is covered with adhesive 48.

FIG. 17 shows the apparatus after evacuation of chamber 6 and beforeactivation of the mechanical pressure inducer 60. FIG. 19 shows the sameapparatus after activation of the mechanical pressure inducer 60 whilethe vacuum pressure inside evacuation chamber 6 is still beingmaintained. In accordance with one preferred embodiment, the vacuumpressure inside evacuation chamber 6 stays constant at 14.7 psithroughout the entire process. This vacuum pressure is applied whileparent structure 52 and repair patch 56 are separated as seen in FIG. 18for a period of time sufficient to remove air and volatiles from theadhesive. When the desired degree of air/volatiles removal has beenachieved, an additive pressure (preferably at least 5 psi) is induced byextending the mechanical pressure inducer 60, as shown in FIGS. 19 and20. During this operation, the vacuum pressure inside chamber 6 ismaintained.

As mechanical pressure inducer 60 is extended, the repair patch 56 isdisplaced downward and pressed against parent structure 52. Asmechanical pressure inducer 60 continues to apply pressure, the adhesive48 applied on the respective confronting surfaces of parent structure 52and repair patch 56 is pressed together for bondline cure as shown inFIG. 20, which is a magnified view of a portion of FIG. 19.

After parent structure 52 and repair patch 56 are pressed together withadhesive 48 therebetween, the adhesive is ready for cure. The cure cyclecan be performed at room temperature or at some elevated temperature,depending on the requirements of the adhesive system. In accordance withthe embodiment depicted in FIGS. 17-20, heating blanket 50 is used toraise the temperature of adhesive 48 to a level higher than roomtemperature. For adhesives that can be cured at room temperature, aheating blanket would not be needed.

In accordance with further alternative embodiments, the linked members62, 64, 66, 68, 70 and 72 shown in FIGS. 17 and 19 (which linked memberslimit lateral displacement of the mechanical pressure inducer) may beeliminated, while a screw mechanism, piston or solenoid is used to pressthe repair patch against the parent structure with adhesivetherebetween. For example, in the case where a solenoid is used, atooling pressure plate can be mounted to the end of the solenoidarmature. Upon activation of the solenoid, the armature extendsdownward, causing the tooling pressure plate to press together thecomponents to be bonded. In accordance with other embodiments, thesolenoid can be replaced by a screw mechanism or a piston.

FIG. 22 is a free body diagram showing the estimated forces exerted forthe exemplary case wherein the strongback support tooling 8 shown inFIG. 19 is a square 12 inches on each side and upper caul plate 38 is asquare 6 inches on each side. In this example, the resulting estimatedcompaction pressure P₂=58.8 psi.

The processes disclosed above allow for both metallic and compositepanel bonding and bonded joints to be fabricated with paste adhesiveswhile minimizing the voids and/or porosity found in the cured bondline.These bonded joints could include test specimens and coupons, quickcomposite repairs, and externally bonded precured patches or uncuredpatches.

The embodiments disclosed above enable the evacuation of trapped airand/or volatiles that could produce a poor bondline once the panels orcomponents (e.g., repair patch and aircraft structure) are bonded inplace. The disclosed embodiments allow the adhesive to remain in anevacuated space through the pre-mating, mating, debulking and cure stepssuch that no entrapped air can encroach into the bondline. The processesdisclosed herein can be employed on aircraft bonded structure, bondedtest specimens or coupons, bonded precured patches, and/or bondeduncured patches.

Some of the embodiments disclosed herein enable void-free bonded jointsin aircraft bonded structure, thus enabling increased reliability infastenerless and unitized structural concepts. Aircraft with weightsavings and cost savings are enabled when the bonded joints can be morereliably produced.

While the invention has been described with reference to variousembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationto the teachings of the invention without departing from the essentialscope thereof. Therefore it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention.

1. An apparatus comprising: a strongback support tool; a spacer that isconnected to one side of said strongback support tool and projects awayfrom said strongback support tool, said spacer extending completelyaround a space adjacent to said one side of said strongback supporttool; an expandable apparatus having a first portion supported by saidstrongback support tool and a second portion that displaces away fromsaid first portion of said expandable apparatus during expansion of saidexpandable apparatus; an upper caul plate carried by said second portionof said expandable apparatus; and a first heating blanket disposedbetween said upper caul plate and said second portion of said expandableapparatus and in contact with an upper surface of said upper caul plate.2: The apparatus as recited in claim 1, wherein said expandableapparatus comprises an inflatable bladder.
 3. The apparatus as recitedin claim 1, further comprising: a first repair patch attached to a lowersurface of said upper caul plate, said first repair patch comprisingfiber-reinforced plastic having uncured resin; and uncured adhesivecovering a surface of said repair patch.
 4. The apparatus as recited inclaim 1, further comprising: a lower caul plate disposed below saidupper caul plate and separated therefrom by a gap; and a second heatingblanket in contact with a bottom surface of said lower caul plate. 5.The apparatus as recited in claim 4, further comprising a collapsibleblock that supports one portion of said upper caul plate and a hingethat supports another portion of said upper caul plate, wherein saidcollapsible block is selected from one of the following group: a papercup, a compression spring, a deflatable ball and sponge material.
 6. Theapparatus as recited in claim 5, further comprising a substratesupporting said lower caul plate, said collapsible block and said hinge.7. An apparatus comprising: a base plate having a surface; a frame incontact with said surface of said base plate along a first path thatsurrounds an area on said surface of said base plate; an expandableapparatus having a first portion supported by said frame and a secondportion that displaces away from said first portion of said expandableapparatus and toward said area on said surface of said base plate duringexpansion of said expandable apparatus; an upper caul plate disposedbetween said expandable apparatus and said base plate; and a firstheating blanket carried by said upper caul plate.
 8. The apparatus asrecited in claim 7, further comprising: a lower caul plate disposedbetween said upper caul plate and said surface of said base plate; and asecond heating blanket disposed between said lower caul plate and saidbase plate.
 9. The apparatus as recited in claim 8, further comprising:a first component supported by said upper caul plate and having asurface; a second component supported by said lower caul plate in aposition whereat a surface of said second component confronts saidsurface of said first component; and adhesive disposed on one or bothconfronting surfaces of said first and second components, wherein saidconfronting surfaces of said first and second components are pressedtogether with said adhesive therebetween after said expandable apparatushas been expanded.
 10. The apparatus as recited in claim 7, wherein saidupper caul plate and said first heating blanket are carried by saidsecond portion of said expandable apparatus.
 11. The apparatus asrecited in claim 7, further comprising collapsible means and hinge meanssupported by said base plate, wherein said collapsible means supportsone portion of said upper caul plate and said hinge means supportsanother portion of said upper caul plate.
 12. The apparatus as recitedin claim 7, further comprising a collapsible block that supports oneportion of said upper caul plate and a hinge that supports anotherportion of said upper caul plate.
 13. The apparatus as recited in claim12, wherein said collapsible block is selected from one of the followinggroup: a paper cup, a compression spring, a deflatable ball and spongematerial.
 14. The apparatus as recited in claim 7, wherein said framecomprises: a strongback support tool and a spacer that is disposedbetween said base plate and said strongback support tool, said spacerbeing in contact with said surface of said base plate along said firstpath. 15: The apparatus as recited in claim 7, wherein said expandableapparatus comprises an inflatable bladder.
 16. The apparatus as recitedin claim 7, further comprising: a vacuum bag overlying said frame andsealed to said surface of said base plate along a second path thatsurrounds said spacer; and a vacuum probe installed in an opening insaid vacuum bag and coupled to a vacuum source.
 17. A repair kitassembled on a surface of a substrate needing repair, said repair kitcomprising: a frame in contact with said surface of said substrate alonga first path that surrounds an area on said surface of said substrate;an expandable apparatus having a first portion supported by said frameand a second portion that displaces away from said first portion of saidexpandable apparatus and toward said area on said surface of saidsubstrate while said expandable apparatus is expanding; a caul platedisposed between said expandable apparatus and said substrate; a heatingblanket carried by said caul plate; a vacuum bag overlying said frameand sealed to said surface of said substrate along a second path thatsurrounds said spacer; a vacuum probe installed in an opening in saidvacuum bag and coupled to a vacuum source; a repair patch supported bysaid upper caul plate; and adhesive covering a surface of said repairpatch or a portion of said surface of said substrate, wherein saidconfronting surfaces of said repair patch and said substrate are pressedtogether with said adhesive therebetween after said expandable apparatushas been expanded.
 18. The repair kit as recited in claim 17, whereinsaid substrate is a part of an aircraft. 19: The repair kit as recitedin claim 17, wherein said substrate and said repair patch are made offiber-reinforced plastic material. 20: The repair kit as recited inclaim 17, wherein said expandable apparatus comprises an inflatablebladder.